The Preston Curve

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The Preston curve describes an empirical relationship between life expectancy and per capita income within a country. It was first proposed by American sociologist Samuel H. Preston in his 1975 paper, "The changing relation between mortality and level of economic development." Preston observed that individuals in wealthier countries typically enjoy longer life spans than those in poorer nations. This is attributed to better access to healthcare, higher education levels, cleaner living environments, and improved nutrition.

Economic Growth and Life Expectancy

Preston's findings indicate that as a poor country's per capita income increases, there is a significant rise in life expectancy. For instance, India's per capita income increased from around ₹9,000 in 1947 to approximately ₹55,000 in 2011, during which the life expectancy of Indians rose from 32 years to over 66 years. Initially, increased income allows people to consume more nutritious food, access better healthcare, and improve overall living conditions, thereby significantly boosting life expectancy.

Flattening of the Curve

However, the relationship between per capita income and life expectancy flattens out after a certain point. This means that further increases in income do not proportionately enhance life expectancy. For example, beyond a certain income threshold, improvements in healthcare and nutrition may yield diminishing returns in extending life expectancy.

Debates and Interpretations

Economists and experts are divided over the causal relationship between income levels and human development indicators. Some argue that promoting economic growth is crucial for improving development outcomes, citing the rapid economic growth of countries like India and China as examples. This perspective suggests that economic growth leads to better health and development indicators.

Others contend that most improvements in life expectancy result from technological advancements rather than purely economic growth. These advancements, such as the development of life-saving vaccines, have increased life expectancy even at low-income levels. Critics of this view argue that technological advancements are also tied to income levels, as wealthier countries have better access to technology.

Conclusion

The Preston curve suggests that poor countries can benefit from technologies developed by richer nations, enabling them to achieve higher life expectancy and better development indicators despite lower income levels.